Feb. 9 (Bloomberg) -- La Nina, the Pacific Ocean cooling
phenomenon that affects weather around the world, is expected
to weaken through the Northern Hemisphere winter and dissipate
by May, the U.S. Climate Prediction Center said.

The weather pattern, which has been blamed for record rain
in Australia and increases the chance of Atlantic hurricanes,
probably will still affect U.S. temperatures and rainfall into
April, said the center, a division of the National Oceanic and
Atmospheric Administration. La Nina is a counterpart of El Nino,
a periodic warming of the Pacific Ocean.

“It’s really too early to know what will happen during
hurricane season” as forecast models from now through June
become less reliable, Michelle L’Heureux, a center
meteorologist, said in a telephone interview from Camp Springs,
Maryland. “I wouldn’t want to rule out anything out for the
hurricane season.”

Temperatures may be above-average in the southeastern and
south-central U.S. into April, while the Northwest will have an
increased chance of below-average temperatures, the center said
in a report today. There may be more precipitation than normal
in the Northwest, Northeast and the Ohio River and Tennessee
River valleys, while the South will probably be drier.

La Nina events occur on an average of every three to five
years and usually last from nine to 12 months. They sometimes
occur in back-to-back years, as is happening now.

Parched Crops

This La Nina has parched crops in Argentina and Brazil and
flooded plantations in Thailand and Malaysia. The phenomenon
also contributed to Australia’s wettest two-year period on
record, as 140.9 centimeters (55.5 inches) of rain fell in 2010
and 2011, the nation’s Bureau of Meteorology said Feb. 7.

La Ninas tend to produce lower vertical wind shear across
the Atlantic, giving hurricanes an expanded area to form. The
2011 hurricane season tied 2010, 1995 and 1887 as the third-most
active on records going back to 1981, spawning 19 named storms
with winds of 39 miles (63 kilometers) an hour or more, NOAA
said. The average season produces 11.